1. Technical Field
Exemplary embodiments of the present disclosure generally relate to a fixing member, a fixing device, and an image forming apparatus.
2. Description of the Related Art
In recent years, electrophotographic image forming apparatuses such as copiers and printers have been directed toward full-color image formation, and the ratio thereof has been gradually increasing. Typically, a color electrophotographic image forming apparatus includes an image forming unit that forms a color image formed of toner images of four colors (cyan, magenta, yellow and black) on a recording medium, and a fixing device that fixes the formed toner images to the recording medium. The fixing device includes a heater for heating the toner images on the recording medium, a fixing member for fixing the toner images to the recording medium, and a pressing member forming a fixing nip between the pressing member and the fixing member. The toner images are fixed to the recording medium by heating and pressing the toner images when the recording medium passes through the fixing nip.
The fixing member having a belt shape or a roller shape is known. The fixing member includes those formed by providing an elastic layer made of a heat-resistant rubber on a base member such as a metal roller or a resin seamless belt, and those formed by further providing a release layer on the elastic layer. Generally, fixing members having the roller shape that are employed are those integrating the heater inside a roller (i.e., heat fixing roller). Further, fixing members having the belt shape that are well known are those providing the heater inside the belt wound around rollers.
The fixing member needs to flexibly adhere to the toner images and efficiently conduct heat so that the toner images of multiple colors (usually toner images of four colors) constituting full color are evenly heated. Thus, a silicone rubber having flexibility and heat resistance is often used for the fixing member. However, silicone rubbers have low thermal conductivity, and thermal conduction to the toner image may become slower.
When thermal conduction is slow, a lot of time is required to heat a surface of the fixing member to a fixing temperature for fixing the toner images. In a case of a high-speed machine, supplying of heat may be too slow. In addition, warm-up speed of the image forming apparatus may become slow. It is important to note that the warm-up speed with respect to temperature increase of the fixing member of the fixing device often limits the rate of warm-up speed of the image forming apparatus, as a whole, when powered on.
As a method to resolve the above-described problems, a technique for shortening the warm-up time (i.e., warm-up speed) of the image forming apparatus is disclosed in related art. In the technique, thermal conductivity of the elastic layer is enhanced by blending carbon fibers in the silicone rubber, and thermal capacity of the elastic layer is reduced by providing hole portions in the silicone rubber. The above-described technique is effective with respect to obtaining high heat dispersion. In addition, by making a thickness of the fixing member thin or by making the fixing belt or the fixing roller have a small diameter, further shortening of warm-up time of the image forming apparatus may be obtained. However, in a case of the fixing member having a small diameter and thin thickness, a heat storage amount is small. Accordingly, if supplying of heat to the fixing nip is not on time, an amount of heat at the surface of the fixing member may be insufficient and fixing performance may decline. In a case of a high-speed machine provided with the fixing member having the small diameter and thin thickness, warm-up speed is fast. However, in an operation of continuously passing through the recording medium through the fixing nip, fixing failure or uneven gloss of an image is generated. More specifically, there is an issue of image failure caused by a lack of the amount of heat at the surface of the fixing member.
A method to resolve the lack of the amount of heat at the surface of the fixing member is disclosed in related art. For example, providing a high thermal conductive layer on a surface layer of the fixing roller, and heating the fixing roller from the outside. With a configuration of the above-described example, heat dispersion is enhanced by the high thermal conductive layer. However, in the configuration, the high thermal conductive layer is a solid silicone rubber or a fluororesin with heat conductive fillers. Accordingly, flexibility of the fixing roller is low. Thus, there is an issue of uneven gloss caused by a lack of following capability of the fixing roller with respect to the toner image.
As described above, the fixing member capable of high-speed warm-up and having good fixing performance is unavailable.